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Thiazolium-ion based organic ionic liquids (OILs).1,2 Novel OILs which promote the benzoin condensation
TETRAHEDRON LETI'ERS
Tetrahedron Letters 40 (1999) 1621-1622
Pergamon
Thiazolium-ion based organic ionic liquids (OILs). t'2 Novel OILs which promote the benzoin condensation. James H. Davis, Jr. *t and Kerri J. Forrester Department of Chemistry, University of South Alabama, Mobile, Alabama 36688-0002 USA
Received 4 December 1998; revised 21 December 1998; accepted 22 December 1998
Abstract 4- and 5-methyl thiazole are readily alkylalexl with n-butyl bromide followed by anion exchange of Br- for BF 4
to give mobile, room-temperature ionic liquids.
These liquids, when treated with small quantities of
triethylamine, serve to promote the benzoin condensation of benzaldehyde. © 1999 ElsevierScienceLtd. All rights reserved. Keywords: ionic liquids; thiazoles; ~ n s a t i o n s ; aldehydes
We have recently initiated research aimed at broadening the structural diversity of ions used for organic ionic liquid (OIL) formation, and to capitalize upon the potential for chemical reactivity by OIL-component ions. The first of these studies, in which we have reported the synthesis of OILs based upon the antifungai drug miconazole, has recently been published [1]. Here, we report the synthesis of two new ionic liquids, each of which acts to promote a classical organic reaction, the benzoin condensation [3,4]. Refluxing
4-methylthiazole
(1)
or
5-
methylthiazole (2) in an excess of n-butyl bromide produces the respective 3-butyl-4/5methylthiazolium bromides in quantitative
isolated as stable, yellow-orange liquids.
Scheme I A..~
n-BuBr N
, NaBF4
A
+
N--~
\
yields [Scheme 1]. After ion exchange with NaBF4 in methanol, the OILs 3 and 4 are '
1 A=H, B=CH3 2 A=CH3, B=H
jdavis @jaguar 1.usouthal.edu
0040-4039/99/$ - see front matter© 1999 Elsevier Science Ltd. All rights reserved. PH: S0040-4039(99)00025 -8
3 A=H, B=CH3 4 A=CH3, B=H
BF4-
1622
The tH-NMR spectra of the compounds are clean save for a small water peak and are consistent with the proposed cation structures, as are the 13C-NMR spectra. FAB-MS data are also in accord with the proposed formulations [5]. After promotion with a small (~ 5 mol %) quantity of triethylamine, OILs 3 and 4 promote the coupling of benzaldehyde to benzoin. The reaction is accomplished when the promoted OIL is stirred under nitrogen as a clearly heterogeneous mixture with a toluene solution of benzaldehyde. Stirring together 1.5 g of either OIL with 200 mL of a 50% (v/v) solution of benzaldehyde in toluene gives in both cases approximately 80% conversion to benzoin after one week. Significantly, continued condensation of benzaldehyde is observed after decantation of the toluene layer from the OIL. We believe this observation to be consistent with a partitioning into the organic phase of the putative thiazolidene-carbene catalyst [Scheme 2].
Scheme 2 benzoin condensation
catalysis
thiazolium cation, and as such represent a
~.
benzaldehyde
1-13Q I~N S--.~ ~ _ _ •" \
departure from common imidazolium- and pyridinium-ion based ionic liquids [2,8]. Additionally, our use of an OIL as a catalyst source compliments the demonstrated utility which ionic liquids exhibit as solvents for
BF4.
base ~
.~C-~_.~,N _~
certain
catalytic
processes [6-8]. To our knowledge, OILs 3 and 4 are the first to be reported which incorporate a
reactions
and
other
Further studies by our
group aimed at expanding the scope of OIL chemistry
are
currently
underway.
References 1.
Davis, J, H., Jr.; Forrester, K. J.; Merrigan, T. Tetrahethon Left. 1998, 39, 8955.
2.
Freemande, M. Chem. Eng. News 1998, 76(13), 32.
3.
Setter, H. Angew. Chem. lnt. Ed. Engl 1976, 5, 639.
4.
Breslow, R.; Schmuck, C. Tetrahedron Lett. 1996, 37, 8241.
5.
Elemental analytical data for both 3 and 4 were invariably outside standard limits, but comport with formulations which include variable amounts of adventitious water, a finding which is consistent with the observed NMR spectra of the species.
6.
Chauvin, Y., Einloft, S.; Ofivier, H. lnd. Eng. Chem. Res. 1995, 34, 2698.
7.
Chanvin, Y.; Olivier-Bourbigou, H. CHEMTECH 1995, 25, 26.
8.
Huddleston, J. G.; Willauer, H. D.; Swatloski, R. P.; Visser, A. E.; Rogers, R. D. J. Chem. Soc., Chem. Commun. 1998, 1765.
Tetrahedron Letters 40 (1999) 1621-1622
Pergamon
Thiazolium-ion based organic ionic liquids (OILs). t'2 Novel OILs which promote the benzoin condensation. James H. Davis, Jr. *t and Kerri J. Forrester Department of Chemistry, University of South Alabama, Mobile, Alabama 36688-0002 USA
Received 4 December 1998; revised 21 December 1998; accepted 22 December 1998
Abstract 4- and 5-methyl thiazole are readily alkylalexl with n-butyl bromide followed by anion exchange of Br- for BF 4
to give mobile, room-temperature ionic liquids.
These liquids, when treated with small quantities of
triethylamine, serve to promote the benzoin condensation of benzaldehyde. © 1999 ElsevierScienceLtd. All rights reserved. Keywords: ionic liquids; thiazoles; ~ n s a t i o n s ; aldehydes
We have recently initiated research aimed at broadening the structural diversity of ions used for organic ionic liquid (OIL) formation, and to capitalize upon the potential for chemical reactivity by OIL-component ions. The first of these studies, in which we have reported the synthesis of OILs based upon the antifungai drug miconazole, has recently been published [1]. Here, we report the synthesis of two new ionic liquids, each of which acts to promote a classical organic reaction, the benzoin condensation [3,4]. Refluxing
4-methylthiazole
(1)
or
5-
methylthiazole (2) in an excess of n-butyl bromide produces the respective 3-butyl-4/5methylthiazolium bromides in quantitative
isolated as stable, yellow-orange liquids.
Scheme I A..~
n-BuBr N
, NaBF4
A
+
N--~
\
yields [Scheme 1]. After ion exchange with NaBF4 in methanol, the OILs 3 and 4 are '
1 A=H, B=CH3 2 A=CH3, B=H
jdavis @jaguar 1.usouthal.edu
0040-4039/99/$ - see front matter© 1999 Elsevier Science Ltd. All rights reserved. PH: S0040-4039(99)00025 -8
3 A=H, B=CH3 4 A=CH3, B=H
BF4-
1622
The tH-NMR spectra of the compounds are clean save for a small water peak and are consistent with the proposed cation structures, as are the 13C-NMR spectra. FAB-MS data are also in accord with the proposed formulations [5]. After promotion with a small (~ 5 mol %) quantity of triethylamine, OILs 3 and 4 promote the coupling of benzaldehyde to benzoin. The reaction is accomplished when the promoted OIL is stirred under nitrogen as a clearly heterogeneous mixture with a toluene solution of benzaldehyde. Stirring together 1.5 g of either OIL with 200 mL of a 50% (v/v) solution of benzaldehyde in toluene gives in both cases approximately 80% conversion to benzoin after one week. Significantly, continued condensation of benzaldehyde is observed after decantation of the toluene layer from the OIL. We believe this observation to be consistent with a partitioning into the organic phase of the putative thiazolidene-carbene catalyst [Scheme 2].
Scheme 2 benzoin condensation
catalysis
thiazolium cation, and as such represent a
~.
benzaldehyde
1-13Q I~N S--.~ ~ _ _ •" \
departure from common imidazolium- and pyridinium-ion based ionic liquids [2,8]. Additionally, our use of an OIL as a catalyst source compliments the demonstrated utility which ionic liquids exhibit as solvents for
BF4.
base ~
.~C-~_.~,N _~
certain
catalytic
processes [6-8]. To our knowledge, OILs 3 and 4 are the first to be reported which incorporate a
reactions
and
other
Further studies by our
group aimed at expanding the scope of OIL chemistry
are
currently
underway.
References 1.
Davis, J, H., Jr.; Forrester, K. J.; Merrigan, T. Tetrahethon Left. 1998, 39, 8955.
2.
Freemande, M. Chem. Eng. News 1998, 76(13), 32.
3.
Setter, H. Angew. Chem. lnt. Ed. Engl 1976, 5, 639.
4.
Breslow, R.; Schmuck, C. Tetrahedron Lett. 1996, 37, 8241.
5.
Elemental analytical data for both 3 and 4 were invariably outside standard limits, but comport with formulations which include variable amounts of adventitious water, a finding which is consistent with the observed NMR spectra of the species.
6.
Chauvin, Y., Einloft, S.; Ofivier, H. lnd. Eng. Chem. Res. 1995, 34, 2698.
7.
Chanvin, Y.; Olivier-Bourbigou, H. CHEMTECH 1995, 25, 26.
8.
Huddleston, J. G.; Willauer, H. D.; Swatloski, R. P.; Visser, A. E.; Rogers, R. D. J. Chem. Soc., Chem. Commun. 1998, 1765.